1. Field of the Invention
The present invention relates to a radiation image obtaining system and a radiation image detector for detecting a radiation image by irradiation of radiation, emitted from a radiation source and which passes through a subject of imaging. Particularly, the present invention relates to a radiation image obtaining system and a radiation image detector for detecting a radiation image of a subject by irradiation of radiation which passes through a grid.
2. Description of the Related Art
In the field of medicine, radiation image obtaining systems are in wide use. The image obtaining systems comprise a radiation source and a radiation image detector. The radiation image detectors comprise a radiation image recording medium such as a stimulable phosphor sheet, a solid state radiation detector or the like, and detect radiation images recorded thereon as electric signals (refer to U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56 (1981)-11395).
Presently, use of the radiation image obtaining systems is not limited to that within imaging rooms of hospitals. For example, the systems are brought into an ICU unit of a hospital to obtain a great number of images within a short period of time. Alternatively, the systems are brought to patients and care recipients outside the hospital, to obtain radiation images at these locations.
Regarding the use of the radiation image obtaining systems described above, there are cases in which imaging is performed with a grid placed between a subject of imaging and the stimulable phosphor sheet, parallel to a recording surface of the radiation image detector. The grid is provided to prevent radiation, which has been dispersed by the subject, from irradiating the stimulable phosphor sheet. The grid is formed by alternately placing lead, which does not transmit radiation, and aluminum or wood, which transmits radiation, at a fine predetermined pitch. When imaging is performed using the grid, the radiation, which has been dispersed by the subject, is less likely to be irradiated onto the stimulable phosphor sheet. Therefore, contrast in the radiation image of the subject can be improved.
Regarding the use of radiation image obtaining systems employing the grids as described above, problems occur in the case that they are brought into the ICU unit to obtain a great number of images in a short period of time, or in the case that they are brought outside the hospital. These problems occur due to the fact that an angle of a central axis of the radiation, emitted from the radiation source, with respect to the radiation image detector cannot be maintained perpendicular. Therefore, the angle may change for every image. Also, the position of the radiation source with respect to the radiation image detector may not be appropriate. The above factors cause the radiation to be incident on the grid from an inappropriate direction, causing problems of false image detection and deterioration of image reproducibility. U.S. Patent Laid-Open No. 20020057762 discloses methods for solving the above problems. The methods disclosed in U.S. Patent Laid-Open No. 20020057762 involve: measuring the angle by using a device such as an electronic level for measuring horizontality or a projection type angle sensor; then adjusting the angle to be substantially perpendicular. However, the manufacturing costs of the system is increased due to the necessity to provide these measuring devices, and the structure of the system becomes complicated.